ignore changelogs and api files for markdown-lint

[Blargian]

Summary

See https://clickhouse-inc.slack.com/archives/C03A9B0H05T/p1740512647178139 for context

• Adds changelogs and generated API files to ignore list for the markdown linter

Checklist

• Delete items not relevant to your PR
• URL changes should add a redirect to the old URL via https://github.com/ClickHouse/clickhouse-docs/blob/main/docusaurus.config.js
• If adding a new integration page, also add an entry to the integrations list here: https://github.com/ClickHouse/clickhouse-docs/blob/main/docs/integrations/index.mdx